Xu Jianzhong: System regulation technology is the key technology of solar thermal power generation

"The core technical problem of solar thermal power generation is the unsteady input of solar energy to the stable output
of electricity.
To achieve this process, it must be supported
by a heat storage system or a controllable auxiliary energy source.
In this process, system control technology is particularly important
.
Academician Xu Jianzhong, President of the Chinese Society of Engineering Thermophysics, said in his report entitled "Technical Challenges of Solar Thermal Power Generation" at the 20th International Congress of Solar Thermal Power Generation and Thermochemistry
.

Xu Jianzhong introduced that solar thermal power generation technology, usually the use of concentrating system to concentrate the direct radiation reflection of the sun to the surface of the heat absorber, solar energy is first converted into heat energy, and stored in the form of heat energy, and then through the steam turbine, gas turbine and other thermal cycle processes, heat energy is converted into mechanical energy, mechanical energy is further converted into electrical energy
.
With the heat storage system, solar thermal power technology can achieve continuous power generation
at night.
The basic physical process of solar thermal power generation is different from conventional thermal power generation only in the way heat energy is obtained
.
When high-quality thermal energy is obtained, the thermoelectric conversion process of solar thermal power generation is exactly the same as that of conventional thermal power plants, coupled with its energy storage system configured according to demand, stable and continuous power output can be achieved, so the quality of its output power is
guaranteed.

The main technical forms of solar thermal power generation are Fresnel type, tower type, trough type, dish type, the difference is mainly in the form of heat collection is different, the basic physical process of power generation is basically the same
.

The main problem facing the use of all renewable energy is, in the final analysis
, cost.
For solar thermal power technology, the main goal is to improve economy
.
From solar energy harvesting to heat transfer to thermoelectric conversion, each link involves components, systems and processes that are the main components of the final cost of
power generation.

The core technical problem of solar thermal power generation is the stable output from the unsteady input of solar energy to the stable output
of electricity.
To achieve this process, it must be supported
by a heat storage system or a controllable auxiliary energy source.
In this process, system control technology is particularly important
.

At present, the technical challenges of solar thermal power generation mainly exist in the following two aspects:

The first is that the development of heat storage technology is relatively slow
.
At present, the main application in solar thermal power stations is double-tank molten salt heat storage technology, and there has been a larger system operation and high-temperature ceramic heat storage technology, but these two technologies only use the sensible heat storage of heat storage materials, and the heat storage density will not be very high
.
Phase change heat storage and chemical heat storage technologies can greatly improve the heat storage density, which make use of the latent heat of the heat storage material and the heat of
chemical reaction respectively.
However, both technologies are currently in the research stage and are still far
from large-scale commercial application.

Another technical challenge of solar thermal power generation lies in the concentrating link, and it is difficult
to improve the heat collection efficiency.
For example, the improvement of the concentration ratio of trough concentrators is limited by geometric optics; Tower solar thermal power generation is limited by cosine efficiency, which makes it difficult to improve the concentration efficiency of large-capacity power stations.
It is also very difficult to improve the high temperature resistance of selectively absorbing coating materials in trough vacuum heat absorbing tubes.
Pressurized air heat absorbers with higher temperature parameters are not currently reliable enough
.

In the face of the above technical challenges, we can currently take the following solutions:

The first is to improve the stability of
solar thermal power generation systems.
Due to the instability of the solar thermal power generation system in the process of start-up, cloud shading and grid dispatching, it is necessary to solve the control problem of each unit of the solar thermal power generation system to achieve the stable operation
of the thermal power generation system.
At the same time, it is also necessary to solve the heat storage problem and ensure the heat energy supply to achieve continuous power generation of solar thermal power generation
systems.

The second is to improve the performance of
heat storage materials.
It is necessary to develop medium and high temperature heat storage materials with good thermal conductivity, high heat storage density and good thermal stability; It is necessary to study the dynamic heat transfer law and strengthening mechanism of heat storage materials during solid-liquid phase transition.
It is necessary to carry out research from integrated design to dynamic regulation and optimization of medium and high temperature heat storage systems with intermittent and unsteady heat sources.
There is a need to investigate controlled chemical heat storage processes
using the heat of reaction of crystal hydrates, inorganic hydroxides, metal hydrides and ammonides.

The third is to improve the reliability
of high-temperature heat absorbers.
Specifically, the coupling heat transfer law of different heat transfer working fluids under the conditions of unsteady state and non-uniform high heat flux density can be studied.
Research on efficient and controllable conversion methods from solar energy to thermal energy; Study the photothermal conversion law and efficiency of different heat absorber structures; The internal thermal stress distribution law of the heat absorber was studied, the plastic failure and creep failure mechanism of the heat absorber material under non-uniform high heat flux density were analyzed, and the prediction method
of the heat absorber life was established.